Equine Genital Squamous Cell Carcinoma: In Situ Hybridization Identifies a Distinct Subset Containing Equus caballus Papillomavirus 2.
Authors: Zhu K W, Affolter V K, Gaynor A M, Dela Cruz F N, Pesavento P A
Journal: Veterinary pathology
Summary
# Editorial Summary Equus caballus papillomavirus 2 (EcPV2) is suspected of driving genital squamous cell carcinoma development in horses, yet establishing causation has been complicated by the virus's frequent presence on normal genital tissue, making PCR detection unreliable for distinguishing infection from transformation. Researchers applied chromogenic in situ hybridisation (ISH) targeting the viral E6/E7 oncogenes to 13 penile and preputial SCCs, a technique offering superior localisation and sensitivity to conventional methods. The ISH approach identified EcPV2 in approximately 46% of tumours (6 of 13 cases), with abundant viral presence throughout neoplastic cells and consistent E6/E7 expression in all metastases examined, whilst the remaining EcPV2-negative cases demonstrated evidence of solar-induced damage as an alternative aetiological pathway. These findings establish EcPV2 as causally implicated in a distinct subset of equine genital SCCs rather than simply an incidental finding, with practical implications for risk stratification, surveillance protocols, and potential future prevention strategies. For equine practitioners, this work underscores the heterogeneous nature of genital SCC aetiology and suggests that histopathological examination complemented by appropriate viral investigation could refine diagnostic accuracy and prognostic understanding of these tumours.
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Practical Takeaways
- •Genital SCC in horses involves two distinct etiologic pathways: EcPV2-associated (approximately 46% of cases) and solar damage-related; understanding which mechanism is present may guide treatment decisions
- •Presence of EcPV2 in normal genitalia does not indicate disease, making ISH or similar techniques necessary to confirm causative role in individual tumours
- •Stability of viral oncogenes in metastases suggests EcPV2-positive SCCs may have consistent molecular characteristics that could inform prognosis and therapeutic approaches
Key Findings
- •In situ hybridization (ISH) detected EcPV2 E6/E7 oncogenes in 6 of 13 genital SCCs, establishing the virus is present within neoplastic cells
- •Solar damage was identified in 6 EcPV2-negative cases, suggesting a distinct pathogenic pathway independent of viral infection
- •Metastatic lesions retained E6/E7 expression, indicating viral genome stability in clonal neoplastic populations
- •ISH technique revealed abundant virus within the majority of neoplastic cells, providing direct evidence for EcPV2's oncogenic role in a subset of cases